Room: AAPM ePoster Library
Purpose: To explore the feasibility of Compton scatter imaging with a photon-counting detector (PCD), for the purpose of turmor tracking during radiation oncology treatment.
Methods: The experimental setup was to simulate kV guidance for lung tumor tracking scenario. With a clinical radiographic system, the primary beam (120kV 200mAs) was collimated into a narrow slit (90mm x 5mm). A Cadmium Telluride (CdTe) based PCD (XC-ACTAEON, Direct Conversion) was used to detect scattered photons at the 90 degree angle from the primary beam path. The active area of the detector is 25.6 x 25.6 mm^2 with pixel dimensions of 0.1 x 0.1 mm^2. To spatially resolve the detected photons, a parallel-hole collimator, with 25 mm thickness, 1 mm hole size and 0.1 mm lead septa, was placed at the front surface of the detector.
To generate more realistic tissue structures around the chest, different phantom objects were placed along the pathway of the primary and scattered photons, including: an 1 cm diameter acrylic rod as the targeted tumor, two layers of 2 cm solid water plates as the chest wall, two layers of 1 cm breast tissue equivalent plates, and a uniform 2.5 cm PMMA plate. The PCD was placed 12 cm from the rod target. Due to its limited view size, the PCD was translated every 2 cm (1 cm around the rod) along the primary beam direction to provide full coverage of all the imaging targets.
Results: The acquired scatter images clearly indicated the locations and dimensions of different objects along the primary beam pathway, including the simulated tumor target. Different tissue types even demonstrated different signal contrast.
Conclusion: The results from this study demonstrated that with the high sensitivity of PCD and strong beam collimation, it is quite promising and feasible to utilize 90-degree-scattered photons for imaging guidance purpose.